For some time now, Ethernet-based data networks which enable cycle times of a few milliseconds have been in use as field buses in automation systems. However, there are applications such as control of complex drive systems, which require much shorter communication cycles in the millisecond range, for example. The control of the drive systems is extremely time critical, i.e., they must be triggered at certain times to prevent malfunctions. A communication system that can transmit real time-critical data in short communication cycles is therefore needed.
To be able to use the Ethernet technology in real time-critical systems, the above-mentioned PROFINET IRT Standard has been introduced. The abbreviation IRT here stands for Isochronous Real Time, i.e., a technology which permits a clock-controlled data transmission in real time.
PROFINET IRT systems make it possible to transmit real time-critical and non-real time-critical data in communication cycles of an adjustable chronological length over a switchable Ethernet data network. To do so, each communication cycle is subdivided into a first time domain, in which real time-critical data can be transmitted, and a second time domain, in which non-real time-critical data can be transmitted. To be able to ensure the required time precision in such a system, the points in time of transmitting or relaying the real time-critical data or real time-critical data telegrams are scheduled. The PROFINET IRT Standard provides in this regard that the forwarding, sending and receiving points in time of the real time-critical data telegrams to be transmitted are saved in all participating coupling equipment and consumers, which capable of relaying, sending and/or receiving the real time-critical data telegrams, and namely more advantageously before the start of the data transmission. Coupling equipment and consumers must therefore be capable of forwarding and/or sending PROFINET IRT data telegrams in the millisecond range. To be able to maintain the precision scheduling of times for transmission and forwarding, the coupling equipment and consumers need special hardware components, which are available on the market. In particular each IRT-capable coupling unit and each IRT-capable consumer have their own clocks, which are synchronized with one another using an essentially known standardized method. Such a method is defined by the IEEE 1588 standard, for example. In order not to interfere with or endanger the required time precision within PROFINET IRT systems, non-IRT-capable equipment, for example, standard Ethernet devices must not be used between the IRT-capable coupling equipment and IRT-capable consumers.
The detailed design and functioning of such a real time-controlled Ethernet data network according to the PROFINET IRT Standard are disclosed in EP 1 388 238 B1, for example, and are sufficiently well known by those skilled in the art.